The American release changed the logo entirely; replaced all mention of Hudson with Jaleco and altered the copyright jargon; and changed the font palette from orange to blue.
"Licensed by Nintendo of America Inc" is shortened to "Licensed by Nintendo".
Bomber King features a "HUDSON PRESENTS" screen upon booting up. Robo Warrior skips it and goes straight to the intro.
In the Japanese version, a bomb blast will kill you instantly (or, at least, remove five tanks from your health). The English release tones it down a notch, merely depleting two tanks, allowing you to survive three blasts right from the start.
All items with Kanji text in Bomber King were modified to visual icons in Robo Warrior.
This one-eyed blob thing was made into a sad face for Robo Warrior. Who knows why.
This chunk of something appears only in Robo Warrior's graphic tiles. It doesn't appear in Bomber King's graphic data. If I had any real experience with the game this would probably go under the Unused Materials banner, but I don't.